Account not active

Hi! I was just wondering if anybody have experienced the same problem as me. I suddenly got the errormessage “This account is not active” when I was about to log in to WP backend. I then tried to upload wp-config.php again and changing the password, but nothing worked.

I don’t know why this happened, does anybody have a solution? Maybe I downloaded a plugin that was no good? My solution for the problem ended up with that I used my second database to register a new account, but lost all content. I just want to know what I have done wrong, so I don’t experience the same problem again, or a solution to the problem.